Field of the Invention
The present invention relates to a control apparatus, a control method, and a driving apparatus for a vibration-type actuator, and an electronic apparatus equipped with a vibration-type actuator.
Description of the Related Art
There is a known vibration-type actuator that makes a vibration body be in pressure contact with a driven body and moves the vibration body and driven body relatively by a vibration excited in the vibration body. When the relative movement of the vibration body and driven body is taken out as an output, a driving target is driven. The vibration body is configured by joining an electro-mechanical energy conversion element, such as a piezoelectric device, to an elastic body. The relative moving speed and moving amount of the vibration body and driven body are controllable by adjusting alternating voltage applied to the electro-mechanical energy conversion element.
When the vibration-type actuator is driven so as to move the driven body (or the vibration body) relatively by a minute distance (hereinafter referred to as a “minute movement”), it may take long time until reaching a target position due to a slow starting motion of the driven body (or the vibration body). Its specific example will be described with reference to FIG. 18A and FIG. 18B.
FIG. 18A is a view schematically showing an example of a driving profile in a case where a controller performs a position feedback control according to an instruction value that is a step signal to move the driven body (or the vibration body) by 2 micrometers. By comparing the instruction value indicated by a solid line with an actual position indicated by a broken line, it is understood that the starting motion takes time.
FIG. 18B is a view showing temporal changes of operation amount for driving the vibration-type actuator. The operation amount increases by integrating position deviations from the start of the instruction value. However, when the operation amount that defines a vibration excited in the vibration body is small, a normal feedback control gain degrades responsiveness. Accordingly, the driven body (or the vibration body) does not start moving until the operation amount reaches a certain amount.
A controller equipped with a gain change means that changes a feedback control gain on the basis of a detection value of relative movement speed of a vibration body and driven body is proposed to solve this problem (see Japanese Laid-Open Patent Publication (Kokai) No. H11-18453 (JP H11-18453A)). Moreover, a controller that controls alternating voltage applied to an electro-mechanical energy conversion element on the basis of a speed command in a low-speed-driving range is also proposed (see Japanese Laid-Open Patent Publication (Kokai) No. 2012-235656 (JP 2012-235656A)).
However, an operation parameter that defines amplitude and shape of a vibration (a shape and size of an elliptic movement) of the vibration body caused in friction sliding surfaces of the driven body and vibration body corresponding to instructed speed and actual speed of the driven body (or the vibration body) at the time of driving the vibration-type actuator has a nonlinear area. Accordingly, the above-mentioned conventional controllers for the vibration-type actuator cannot obtain sufficient responsiveness for the minute movement when only the feedback control gain or the voltage applied to the electro-mechanical energy conversion element is changed.